Systems approaches reveal that ABCB and PIN proteins mediate co-dependent auxin efflux

Abstract

Members of the B family of membrane-bound ATP-binding cassette (ABC) transporters represent key components of the auxin-efflux machinery in plants. Over the last two decades experimental studies have shown that modifying ABCB expression affects auxin distribution and plant phenotypes. However, precisely how ABCB proteins transport auxin in conjunction with the more widely studied family of PIN-formed (PIN) auxin efflux transporters is unclear, and studies using heterologous systems have produced conflicting results. Here, we integrate ABCB localization data into a multicellular model of auxin transport in the Arabidopsis thaliana root tip to predict how ABCB-mediated auxin transport impacts organ-scale auxin distribution. We use our model to test five potential ABCB–PIN regulatory interactions, simulating the auxin dynamics for each interaction and quantitatively comparing the predictions with experimental images of the DII-VENUS auxin reporter in wild type and abcb single and double loss-of-function mutants. Only specific ABCB–PIN regulatory interactions result in predictions that recreate the experimentally observed DII-VENUS distributions and long-distance auxin transport. Our results suggest that ABCBs enable auxin efflux independently of PINs; however, PIN-mediated auxin efflux is predominantly through a co-dependent efflux where co-localised with ABCBs.

RootSlice—A novel functional‐structural model for root anatomical phenotypes

“…The main differences between these alternatives lie in the geometrical representation of individual cells and the way physical and chemical interactions among cells are handled (Band et al, 2012a). Early multicellular models used a structured rectangular grid to depict root topologies (Grieneisen et al, 2007; Mähönen et al, 2014; Mironova et al, 2012), however, recent models use realistic root anatomies, derived either from digitised microscopic images (Band et al, 2012a; Mellor et al, 2016, 2022; Moore et al, 2015, 2017) or idealised using computational tools (Di Mambro et al, 2017). Different frameworks to develop multicellular models exist, namely CellModeller (Dupuy et al, 2008, 2010), OpenAlea (Collis et al, 2022; Pradal et al, 2008), VirtualPlantTissue (De Vos et al, 2017; Merks et al, 2011) and MECHA (Couvreur et al, 2018).…”

Auxin regulation on crop: from mechanisms to opportunities in soybean breeding

“…ABCB19 co-localizes and stabilizes PIN1 in membrane lipid microdomains to enhance PIN1 transport activity (Titapiwatanakun et al 2009). Computational modelling further supports the synergistic interactions of ABCB and PIN proteins for directional auxin ow (Mellor et al 2022). Beside of auxin export system, auxin uptake is also an active process which requires proton motive force.…”

ABCB‐mediated shootward auxin transport feeds into the root clock

“…Genetic and biochemical studies have indicated a tight interplay between both PINs and ABCBs (Bandyopadhyay et al, 2007;Blakeslee et al, 2007;Mravec et al, 2008;Deslauriers & Spalding, 2021). A recent simulation of auxin transport in the root meristem identified strong PIN-ABCB co-dependent auxin efflux, in combination with individual auxin transport activities, and fluxes via plasmodesmata as the most likely scenario underpinning auxin transport in the root tip (Mellor et al, 2020(Mellor et al, , 2022. The proposed auxin transport components of the reverse fountain are AUX1, for auxin uptake, in combination with PIN1, PIN2, PIN3, PIN4, PIN7, ABCB1, ABCB19, and ABCB4 for auxin efflux.…”